1. Field of the Invention
The present invention relates to a method and a catalyst composition for preparing amides, and more particularly, to a method and a catalyst composition having an ionic liquid and a Bronsted acid for catalyzing ketoximes to produce amides.
2. Description of the Prior Art
Caprolactam is an important raw material in the manufacture of nylon 6 fibers and thin films. Beckman rearrangement of cyclohexanone oxime is an important reaction step in producing caprolactam. Currently, oleum is used as a catalyst for converting cyclohexanone oxime to caprolactam sulfate during Beckman rearrangement, and then ammonia is used for neutralization, so as to obtain caprolactam. While the conversion rate of cyclohexanone oxime is almost 100% and the selectivity for caprolactam is 99%, a large amount of low-valued ammonium sulfate is generated during the reaction, and concentrated sulfuric acid used for catalysis causes problems such as corrosion to the whole equipment and environmental pollution. In the recent years, researches on new production technologies of caprolactam focus on reducing or avoiding the generation of the by-product, ammonium sulfate. Moreover, compared with the gas phase reaction, liquid-phase rearrangement has advantages including moderate reaction conditions, fewer requirements to the equipments, etc., and is advantageous to the reconstruction of the current equipments. As a result, scholars worldwide have put efforts on developing liquid-phase rearrangement, and attained substantial developments and breakthrough. For example, in Chinese Patent No. 1852898A assigned to Sumitomo Chemical Company Ltd. in Japan, an ionic liquid having the sulfonate group is used as a catalyst to give the selectivity of caprolactam up to 99%. In Chinese Patent No. 1919834 assigned to Lanzhou Institute of Chemical Physics in China, an ionic liquid having sulfuryl chloride is used as a catalyst to give the selectivity of caprolactam up to 97.2%. In WO2008/145312A1 assigned to DSM N.V. in Netherlands, an anionic solution having sulfate is used for conversion reaction to give the selectivity of amide up to 99%.
However, in the above-mentioned patents, the acidic ionic liquid is used for catalyzing the conversion reaction, such that if caprolactam is not efficiently separated, there would be a chemical binding between caprolactam and the ionic liquid, and furthermore viscosity of the ionic liquid would be increased, resulting in blocking pipes, which is disadvantageous to fabrication.
Accordingly, there is an urgent need of a catalyst composition for preparing amides which effectively decreases viscosity of an ionic liquid and has high conversion rate of ketoximes and high selectivity of amides.